Method of making a heat exchanger coil assembly

ABSTRACT

Method of making a heat exchanger coil assembly for a steam generator including coil turns arranged in concentric layers and spaced apart by spacer members, and including the step of dip soldering the assembly for securing the turns and spacer members together to form a unitized assembly and to anneal the assembly.

United States Patent 1151 3,639,963 Maher 1 Feb. 8, 1972 [54] METHOD OF MAKING A HEAT 1,692,818 11/1928 Christoph ..29/157.3 B EXCHANGER COIL ASSEMBLY 2,136,153 11/1938 Rosenblad ...29/l57.3 X 2,160,644 5/1939 Clarkson ....122/250 [72] Frank Mount Prospect, 2,508,247 5/1950 Giauque ....165/145 [73] Assignee: Vapor Corporation, Chicago, 111. 3,282,257 1 H1966 Mclnemey et al... ..122/250 3,357,484 12/1967 Maher ..29/l57.3 C [221 1969 3,086,358 4/1963 Tumauicus ..29/157.3 ux [21] Appl. No.: 868,970

Primary Examiner-lohn F Campbell Related Application Dam Assistant Examiner-D. C. Reiley 2] i i i of Ser- No 717 51 p 1 19 8 aban Attorney-Julian Falk, Chester A. Williams, .|l'., Marshall J.

doned Breen and Kinzer, Dom & Zickert [521 US. Cl ..29/1s7.3 R, 29/010. 4, 165/162 1571 ABSTRACT [51] Int. Clof h g a eat exchanger coil assembly for a steam [58 Field ofSearch ..29/157.3, 1571.250i 3101.643, generator including co mms arranged in concentric layers and spaced apart by spacer members, and including the step of dip soldering the assembly for securing the turns and spacer [56] References cued members together to form a unitized assembly and to anneal UNITED STATES PATENTS the assembly- 3,349,842 10/1967 Prybil 165/163 4 Claims, 3 Drawing Figures PATENTED FEB 8 I972 SHEET 1 OF 2 FIG! FRANK A. MAHER ATTORNEY sum 2 OF 2 PATENTED FEB 8 I972 ll] /EHTG FRANK A. MAH BY V ATTORNEY METHOD OF MAKING A HEAT EXCHANGER OIL ASSEMBLY This application is a division of my copending application Ser. No. 717,516, filed Apr. 1, 1968, now abandoned.

This invention relates in general to steam generators, and more particularly to a heat exchanger for use in a steam generator, and still more particularly to a method of making a heat exchanger coil assembly for a heat exchanger.

The heat exchanger coil assembly of the present invention is adapted to be enclosed in a suitable housing to define a heat exchanger that functions to transfer heat from the steam generator condensate generator return line to the steam generator feed water. The coil assembly is connected to the hot condensate return line of the steam generator while the housing of the heat exchanger is connected to the cold feed waterline. Condensate return water is cooled while feed water is preheated by the heat exchanger.

Heat exchanger coil assemblies heretofore made have encountered early failure difficulties especially caused by mechanical vibrations and/or thermal expansion and contraction between mating parts. Moreover, it has been costly to perform spot annealing of localized areas on the tubing at brazed locations.

The present invention obviates the above difficulties in providing an improved heat exchanger coil assembly and method of making same that effectively increases the service life of the assembly over heretofore known assemblies. Further, a unitized assembly is provided that is resistant to failure due to mechanical vibrations and/or thermal expansion and contraction between mating parts. The assembly is first made by winding a length of tubing to provide a plurality of coil turns having concentric rows and staggered layers. During the winding of the coils, sinuous spacers are strategically located between the concentric rows of turns, which spacers effectively space the rows from each other and also space the layers from each other. One piece fittings are then brazed to the terminal ends of the coil turns. The coil is then preheated and prepared for dip soldering by dipping into a solution of a suitable type. Thereafter the assembly is dipped into a bath of molten solder at a predetermined temperature for a predetermined period of time to uniformly anneal the tubing and the brazed connections, as well as to unite the spacers with the coil turns. Upon removal from the bath of molten solder, the curing of the solder completes the method of making the assembly, wherein a uniformly annealed and unitized assembly which is not subject to wear caused by movement of mating parts is provided.

Accordingly, it is an object of the present invention to provide an improved heatexchanger coil assembly for use in a heat exchanger of a steam generator.

It is a further object of this invention to provide a method of making a heat exchanger coil assembly that reduces manufacturing, labor and material costs, and provides an assembly having a greater service life over heretofore known assemblies.

Another object of this invention is in the provision of a heat exchanger coil assembly that is a unitized structure not effected by mechanical vibrations and/or thermal expansion or contraction between mating parts.

Another object of this invention resides in the provision of a heat exchanger assembly that is uniformly annealed by dipping in a molten of solder for a predetermined time at a predetermined temperature.

Other objects, features and advantages of the invention will be apparent from the following detailed disclosure, taken in conjunction with the accompanying sheets of drawings, wherein like reference numerals refer to like parts, in which:

FIG. 1 is a top plan view of the heat exchanger coil assembly according to the present invention;

HO. 2 is an axial sectional view taken through the coil assembly of FIG. 1 and substantially along line 2-2 thereof; and

FIG. 3 is a detailed vertical sectional view of one of the fittings and taken substantially along line 3of FIG. 1.

Referring now to the drawings, the heat exchanger coil assembly of the present invention, generally indicated by the numeral 10, is formed to provide a plurality of concentric rows of coil turns ll, 12, 13 and 14. As seen in FIG. 2 staggered layers of coil turns are defined from top to bottom. The tubing may be of any suitable material, such as copper, and would be initially a straight length of tubing that is wound by a suitable machine to form the coil assembly as seen in the drawings. The coil turns are formed to provide an annular coil assembly having inner and outer concentric faces and opposed frustoconical end faces. The turns are defined by a continuous length of tubing which terminate in ends 15 and 16 at one of the end faces of the coil assembly. One of the ends would constitute an inlet condensate return water end while the other would constitute an outlet condensate return water end. During the winding of the tubing, sinuous spacers 17, 18 and 19 are strategically located between adjacent rows of coil turns to provide the proper spacing between adjacent rows and the proper spacing between adjacent layers. The pattern of spacer location is illustrated in F IG. 1, although it may be appreciated that it might vary somewhat from this pattern.

Completion of the winding of the tubing to form the coil shape as seen in FIG. 2 provides a four-pass heat exchanger I system wherein the concentric rows may be defined as an inner row 11, an'inner intermediate row 12, an outer intermediate row 13 and an outer row 14. Following formation of the tubing, fittings 20 and 21 are secured to the terminal ends.

15 and 16, respectively. While the fittings are slightly different in size, they are essentially of the same type.

The fitting 20 includes a cylindrical body 22 having an external shoulder 23 formed to have abut thereagainst a square locating plate 24. The locating plate is brazed to the fitting and serves to provide a means of holding the coil to prevent twisting and damage of the coil during assembly. The upper external surface of the body 22 is threaded at 25 to facilitate connecting to suitable lines. A longitudinally extending blind bore 26 extends inwardly and downwardly from the discharge end 27 to a bottom wall 28 of the body. A stepped bore 29 extends substantially normal to the blind bore 26 and is provided at the bottom of the fitting to receive the terminal end 15 of the coil.. The stepped bore 29 intercommunicates with the blind bore 26 and therefore defines a passageway through the fitting. A shoulder 30 is defined by the stepped bore 29 to provide a stop against which the terminal end 15 abuts during placement of the fitting thereon. The size of the stepped bore is such as to snugly receive the terminal end of the tubing, and the fitting and tubing are secured together by brazing, wherein the elongated fitting body 22 extends substantially parallel to the longitudinal axis of the coil and also substantially coaxial with the center line of the coil. The shoulder 30, defining a positive stop for the tubing as it is inserted into the stepped bore 29 insures that the tubing is not inserted too deep which would possibly eliminate the smooth transitional design of the fitting. It is noted that the tubing is stopped short of the blind bore 26. Thus, a smooth flow transition is established from the piping external of the assembly into the assembly and back to the external piping. The depth of the drilled holes providing the blind bore and the stepped bore are accurately controlled.

The fitting 21 is substantially the same as the fitting 20 and includes an elongated body 31 having an external flange 32 defining a stop against which a square locating plate 33 may abut. The plate 33 is suitably brazed to the fitting and to the flange 32. The upper external surface of the fitting is threaded at 34 to facilitate connection to external piping. An elongated blind bore 35 is drilled in the fitting and extends downwardly from the upper discharge end 36 to a bottom wall 37. A stepped bore 38 is provided at the bottom of the fitting and extends normal to the blind bore 35, and defines a shoulder 39 which provides a positive stop for the tubing end 16 that is thereafter brazed to the fitting. The fitting 21 is also oriented to extend substantially parallel to the longitudinal axis of the coil assembly. Like the fitting 20 relative to the coil turns, the fitting 21 provides a smooth flow transition from the external piping into the heat exchanger and back to the external piping. The shoulder 39 is arranged to stop the end 16 just short of the blind bore 35;

After the coil assembly consisting of the tubing, the sinuous spacers, and the fittings is assembled, the assembly is prepared for dipping into a molten bath of soft solder. In preparing the assembly, the coil is preheated and dipped into a surface conditioning solution. Thereafter, the assembly is dipped into a bath of molten solder at a specified temperature and for a specified time to allow solder connections at all mating surfaces between the coil turns and spacers to thereby provide a unitized coil assembly and also to uniformly anneal the tubing and brazed connections. The assembly is submerged into the bath of solder with the exception of the threaded ends of the fittings. Annealing of the brazed connections eliminates the need thereafter to spot anneal the connections. Accordingly, a unitized assembly, uniformly annealed is defined which increases the service life of the coil assembly.

It will be understood that modifications and variations may be effected without departing from the scope of the novel concepts of the present invention.

I claim:

1.,A method of making a heat exchanger coil assembly for a steam generator from a length of tubing and fittings comprising the steps of winding the tubing into a plurality of coil turns arranged in concentric rows and staggered layers defining an annularly shaped coil having inner and outer concentric faces and opposed end faces, locating spacers between adjacent rows, placing the fittings on the terminal ends of said turns, connecting the fittings to said terminal ends, preparing said assembly for a molten solder dip, dipping the assembly except for the ends of the fitting into a bath of molten solder for a predetermined period of time to secure the spacers and turns together by producing solder connections at all mating surfaces therebetween and provide a unitized coil assembly and to uniformly anneal the coil turns and the connections.

2. A method as defined in claim 1, wherein said step of preparing the assembly for the solder dipping step includes the step of preheating the assembly.

3. A method as defined in claim 2, wherein said step of preparing the assembly for the solder dipping step further includes the step of preconditioning the surface of the assembly prior to the solder dipping step.

4. A method as defined in claim I, wherein said step of connecting the fittings to said terminal ends further includes the step of brazing the fittings to the terminal ends. 

1. A method of making a heat exchanger coil assembly for a steam generator from a length of tubing and fittings comprising the steps of winding the tubing into a plurality of coil turns arranged in concentric rows and staggered layers defining an annularly shaped coil having inner and outer concentric faces and opposed end faces, locating spacers between adjacent rows, placing the fittings on the terminal ends of said turns, connecting the fittings to said terminal ends, preparing said assembly for a molten solder dip, dipping the assembly except for the ends of the fitting into a bath of molten solder for a predetermined period of time to secure the spacers and turns together by producing solder connections at all mating surfaces therebetween and provide a unitized coil assembly and to uniformly anneal the coil turns and the connections.
 2. A method as defined in claim 1, wherein said step of preparing the assembly for the solder dipping step includes the step of preheating the assembly.
 3. A method as defined in claim 2, wherein said step of preparing the assembly for the solder dipping step further includes the step of preconditioning the surface of the assembly prior to the solder dipping step.
 4. A method as defined in claim 1, wherein said step of connecting the fittings to said terminal ends further includes the step of brazing the fittings to the terminal ends. 